Lecture 48: Fertilisation Implantation Gastulation Flashcards
(31 cards)
what day does ovulation occur in a menstrual cycle
day 14 of 28
when does sperm need to arrive in female reproductive tract in order to be successful
ovulation +/- 1-2 days
of the 4-5mil sperm ejaculated how many actually reach site of fertilisation
300-500 (1%)
what happens to the cervical mucus during ovulation and why
- ^ in amount
- becomes less thick
- becomes less acidic
- allows for easier transport of sperm
how long can sperm survive in the female reproductive tract
5 days
outline the process of capacitation
- sperm membrane molecules masked by plasma proteins
- spermatozoa cannot fertilise oocytes when newly ejacualted due to plasma prots
- in uterus and oviduct plasma prot covering is removed
- binding portions of sperm head exposed
- process can take 5-7hrs
where on the oocyte does spermatozoa bind to
zona pellucida
what does passage of sperm through cumulus layer of oocyte depend on
- hyaluronidase released from sperm acrosome
- tubal mucosal enzymes
- flagellar action
what is the cloudy layer of cells around the oocyte called
cumulus layer of cumulus cells (or corona radiatus)
outline the binding of sperm to the zona pellucida
- zona pellucida is a glycoprotein shell (facilitates and maintains sperm binding and induces acrosome reaction)
- capacitated sperm can penetrate cumulus oophorus and adhere to ZP
- multiple adhesions to ZP triggers acrosome reaction
- ZP binding triggers opening of Ca2+ channels in sperm cell membrane driving exocytosis of acrosomal contents
- acrosome reaction is prerequisite for sperm to fuse w/ oocyte plasma membrane
what is an acrosome
modified lysosome located around anterior of sperm head
outline what happens when a sperm binds to the oocyte plasma membrane
- sperm binding to ZP results in cortical reaction
- exocytosis of cortical enzymes into ZP
- destroys sperm receptors on zona pellucida
- causes hardening of zona pellucida (zona reaction)
- slow block to polyspermy (fertilisation envelope)
what happens when more than one sperm manages to enter ovum
foetus nearly always aborts
what happens at stages 3 and 4 of fertilisation
- fusion of plasma membranes of oocyte and sperm
- triggers completion of meiosis 2 (mature ovum + second polar body)
- head and tail of sperm enters cytoplasm of oocyte
what is the 5th stage of fertilisation
formation of male and female pronuclei
outline 5th stage of fertilisation
- pronuclei each contain 23 chromosomes
- male and female pronuclei indistinguishable
- membranes of pronuclei breakdown
- chromosomes become arr. for mitotic cell division (first cleavage division)
- fertilisation complete
what is a fertilised egg called
zygote
describe the results of fertilisation
- stimulates secondary oocyte to complete meiosis
- restoration of diploid number of chromosomes (46)
- variation of human species as maternal and paternal chromosomes intermingle
- determination of sex
- initiation of cleavage
what is cleavage
- series of mitotic divisions
- resulting cells (blastomeres) become smaller w/ each division
- after 3 divisions blastomeres undergo compaction
- compact blastomeres divide to form 16 cell morula
what is the name of the cells resulting from cleavage
blastomeres
describe a blastocyst
- embryo between 5-7days following fertilisation
- 2 distinct cell types
- central cavity filled w/ fluid (blastocoel)
- hatches from zona pellucida prior to implantation
name the outer and inner cell mass of the blastocyst
outer = trophoblast inner = embryo blast
describe what happens to the blastocyst in implantation
- when implantation begins:
- trophoblast cells divide and differentiate
- -> outer syncytiotrophoblasts
- -> inner cytotrophoblasts
- embryo blast cells divide and differentiate
- -> epiblast
- -> hypoblast
what phase is the uterus in at time of implantation
secretory phase
